Implement select tool tests and modify test utilities

[RahulHi]

This PR implements some tests for the select tool, particularly to test for the correct behavior when using the undo/redo functionalities.

This PR additionally improves the testing utilities:

• The move_mouse function now accepts an EditorMouseState as input to avoid discarding the previous mouse state as that may result in unintended behavior.
• Adds test utilities for the dispatcher.

Part of #595